No evidence of fascicular injury following a low-volume intraneural injection of the median nerve: a cadaveric study.

BACKGROUND: The test dose or hydrolocation technique allows rapid detection of spread location. Though its primary aim is to enhance safety in peripheral nerve blocks, evidence on the potential risks of an intraneural test aliquot is lacking. We conducted a cadaveric study to evaluate the risk of fascicular injury following a low-volume (<1 mL) intraneural injection of the median nerve. METHODS: Ten upper limbs from fresh unembalmed human cadavers were studied. In-plane ultrasound-guided intraneural injections of the median nerve were performed at mid, proximal, and distal locations using 1 mL of methylene blue and heparinized blood solution. Nerves were extracted and samples immersed in 10% buffered formalin for 4 weeks. Perpendicular 3 mm slices were obtained for H&E staining and light microscopy analysis. Our main objective was to assess the number of injured fascicles. Secondarily, we evaluated the pattern of intraneural spread. Fascicular injury was defined as the presence perineurium or axonal disruption and/or the presence of erythrocytes inside a nerve fascicle. RESULTS: Thirty injections were performed in 10 median nerves. Sonographic swelling was confirmed in 100% of the cases. 352 histological sections were analyzed to assess study outcomes. The mean number of fascicles on each section of median nerve was 20±6 covering 49%±7% of the nerve area. No evidence of axonal disruption nor intra-fascicular erythrocytes was found in any of the analyzed sections. CONCLUSIONS: Low-volume intraneural injections do not result in evident fascicular injury. Our findings support the use of a test dose in ultrasound-guided regional anesthesia.

Spread of local anesthetic injected in the paravertebral space, intertransverse processes space, and erector spinae plane: a cadaveric model.

INTRODUCTION: Paraspinal fascial plane blocks have become popular and include the erector spinae plane (ESP) and intertransverse process (ITP) blocks. Controversy exists regarding the exact mechanism(s) of these blocks. We aimed to evaluate the spread of local anesthetic (LA) following ESP and ITP blocks as compared with paravertebral (PV) blocks in a cadaveric model. METHOD: Single-injection ultrasound guided ESP (n=5), ITP (n=5), and PV (n=5) blocks were performed in 15 fresh cadaver hemithoraces. The extent of LA spread within the erector spinae fascial plane, involvement of the dorsal ramus, and distribution within the PV space, were qualitatively described. RESULTS: The spread of LA following ESP block extended eight vertebral levels in a cranio-caudal direction, involving the dorsal ramus at each level, but without LA spread into the PV space nor to the ventral rami. LA spread following ITP block extended 1-2 vertebral levels within the PV space and 7 vertebral levels within the erector spinae fascial plane. The spread of LA following PV blocks extended 2-4 vertebral levels, involving the ventral and dorsal ramus at each level, but without LA spread into the ESP. CONCLUSION: Based on the results of this cadaveric experimental model of paraspinal fascial plane blocks, LA spread following ITP blocks extends into both the PV space and the erector spine fascial plane, and thus may offer a more favorable analgesic profile than ESP blocks.

Anatomic barriers to paraspinal blocks: a cadaver case series

Abstract The paraspinal space is intriguing in nature. There are several needle tip placements described in compact anatomical spaces. This has led to an incertitude regarding the appropriate anatomic locations for needle tip positions. Through our cadaver models we try to resolve the issues surrounding needle tip positions clarifying anatomical spaces and barriers. Further we propose an anatomical classification based on our findings in cadaveric open dissections and cross and sagittal sections.

Clavipectoral fascia plane block spread: an anatomical study.

BACKGROUND: The clavipectoral fascia plane block (CPB) is a novel anesthetic management strategy proposed by Valdes-Vilches for clavicle fractures. This study aimed to investigate the distribution of the injected solution around the clavicle and the surrounding tissues. METHODS: Twelve clavicle samples were acquired from six cadavers. CPB was conducted using a 20 mL solution comprising methylene blue and iodinated contrast agent to improve visibility of the injected substance's dispersion. Methylene blue spread was assessed through anatomical dissection across distinct planes (subcutaneous, superficial muscular, deep muscular, and periosteal layers of the clavicle) in five cadavers. For the purpose of comparing methylene blue distribution, CT scans were performed on three cadavers. RESULTS: Methylene blue was detected in the medial, intermediate, and lateral supraclavicular nerves, as well as superficial muscles including the deltoid, trapezius, sternocleidomastoid, and pectoralis major. However, no staining was observed in the deep muscle plane, including the subclavius, pectoralis minor, and clavipectoral fascia (CPF). Anterosuperior periosteum exhibited staining in 54% of surface, while only 4% of the posteroinferior surface. CT images displayed contrast staining in anterosuperior periclavicular region, consistent with observations from sagittal sections and anatomical dissections. CONCLUSION: The CPB effectively distributes the administered solution in the anterosuperior region of the clavicular periosteum, superficial muscular plane, and supraclavicular nerves. However, it does not affect the posteroinferior region of the clavicular periosteum or the deep muscular plane, including the CPF.

The size, number, and distribution of nerve endings around and within the human epiglottis, focusing on tracheal intubation maneuvers.

The aim of this study was to examine the distribution of nerve endings in the mucosa, submucosa, and cartilage of the epiglottis and the vallecula area and to quantify them. The findings could inform the choice of laryngoscope blades for intubation procedures. Fourteen neck slices from seven unembalmed, cryopreserved human cadavers were analyzed. The slices were stained, and cross and longitudinal sections were obtained from each. The nerve endings and cartilage were identified. The primary metrics recorded were the number, area, and circumference of nerve endings located in the mucosa and submucosa of the pharyngeal and laryngeal sides of the epiglottis, epiglottis cartilage, and epiglottic vallecula zone. The length and thickness of the epiglottis and cartilage were also measured. The elastic cartilage of the epiglottis was primarily continuous; however, it contained several fragments. It was covered with dense collagen fibers and surrounded by adipose cells from the pharyngeal and laryngeal submucosa. Nerve endings were found within the submucosa of pharyngeal and laryngeal epiglottis and epiglottic vallecula. There were significantly more nerve endings on the posterior surface of the epiglottis than on the anterior surface. The epiglottic cartilage was twice the length of the epiglottis. The study demonstrated that the distribution of nerve endings in the epiglottis differed significantly between the posterior and anterior sides; there were considerably more in the former. The findings have implications for tracheal intubation and laryngoscope blade selection and design.

Anatomic barriers to paraspinal blocks: a cadaver case series.

The paraspinal space is intriguing in nature. There are several needle tip placements described in compact anatomical spaces. This has led to an incertitude regarding the appropriate anatomic locations for needle tip positions. Through our cadaver models we try to resolve the issues surrounding needle tip positions clarifying anatomical spaces and barriers. Further we propose an anatomical classification based on our findings in cadaveric open dissections and cross and sagittal sections.

Ultrasound evaluation of a new surface reference line to describe sural nerve location and safe zones to consider in posterior leg approaches.

PURPOSE: Several authors have described methods to predict the sural nerve pathway with non-proportional numerical distances, but none have proposed a person-proportional, reproducible method with anatomical references. The aim of this research is to describe ultrasonographically the distance and crossing zone between a surface reference line and the position of the sural nerve. METHODS: Descriptive cross-sectional study, performed between January and April 2022 in patients requiring foot surgery who met inclusion criteria. The sural nerve course in the posterior leg was located and marked using ultrasound. Landmarks were drawn with a straight line from the medial femoral condyle to the tip of the fibula. Four equal zones were established in the leg by subdividing the distal half of the line. This way, areas based on simple anatomical proportions for each patient were studied. The distance between the marking and the ultrasound nerve position was measured in these 4 zones, creating intersection points and safety areas. Location and distances from the sural nerve to the proposed landmarks were assessed. RESULTS: One-hundred and four lower limbs, 52 left and 52 right, assessed in 52 patients were included. The shortest median distance of the nerve passage was 2.9 mm from Point 2. The sural nerve intersection was 60/104 (57.7%) in Zone B, 21/104 (20.1%) in Zone C and 19/104 (18.3%) in Zone A. Safety zones were established. Average 80.5% of coincidence in sural nerve localization was found in the distal half of the leg, in relation to the surface reference line when comparing both legs of each patient. CONCLUSIONS: This study proposes a simple, reproducible, non-invasive and, for the first time, person-proportional method, that describes the distance and location of the main areas of intersection of the sural nerve with points and zones (risk and safe zones) determined by a line guided by superficial anatomical landmarks. Its application when surgeons plan and perform posterior leg approaches will help to avoid iatrogenic nerve injuries. LEVEL OF EVIDENCE: IV.

Ultrasound is better than injection pressure monitoring detecting the low-volume intraneural injection.

INTRODUCTION: Inadvertent intraneural injection is not infrequent during peripheral nerve blocks. For this reason, injection pressure monitoring has been suggested as a safeguard method that warns the clinician of a potentially hazardous needle tip location. However, doubts remain whether it is superior to the sonographic nerve swelling in terms of earlier detection of the intraneural injection. METHODS: An observational cadaveric study was designed to assess injection pressures during an ultrasound-guided intraneural injection of the median nerve. We hypothesized that the evidence of nerve swelling occurred prior to an elevated injection pressure (>15 pound per square inch) measured with a portable in-line monitor. 33 ultrasound-guided intraneural injections of 11 median nerves from unembalmed human cadavers were performed at proximal, mid and distal forearm. 1 mL of a mixture of local anesthetic and methylene blue was injected intraneurally at a rate of 10 mL/min. Following injections, specimens were dissected to assess spread location. Video recordings of the procedures including ultrasound images were blindly analyzed to evaluate nerve swelling and injection pressures. RESULTS: 31 injections were considered for analysis (two were excluded due to uncertainty regarding needle tip position). >15 pound per square inch was reached in six injections (19%) following a median injected volume of 0.6 mL. Nerve swelling was evident in all 31 injections (100%) with a median injected volume of 0.4 mL. On dissection, spread location was confirmed intraneural in all injections. DISCUSSION: Ultrasound is a more sensitive and earlier indicator of the low-volume intraneural injection than injection pressure monitoring.

Accuracy of ultrasonography predicting spread location following intraneural and subparaneural injections: a scoping review.

INTRODUCTION: Ultrasonography is useful for detecting intraneural injections. However, the reliability of the sonographic findings of intraneural and subparaneural injections in terms of true spread location and their association with intrafascicular deposits has not been systematically evaluated. EVIDENCE ACQUISITION: Our objectives were: 1) to explore the reliability of sonographic findings of intraneural and subparaneural injections when validated with tests of true spread such as histology, dissection, or imaging; and 2) to evaluate their association with intrafascicular deposits. A scoping review was conducted according to Joanna Briggs guidelines. Cinahl, PubMed, ProQuest, ScienceDirect, Scopus and Cochrane databases were searched for studies on adults, cadavers, and animal models. Pediatric studies were excluded. EVIDENCE SYNTHESIS: The search strategy found 598 citations. Following screening, 19 studies were selected. Intraneural injections occurred in the brachial plexus, sciatic, femoral, and median nerves. Subparaneural injections in popliteal, supraclavicular and interscalene blocks. Sixteen different ultrasound findings were used to label injection location. Subepineural deposits within individual nerves occurred occasionally following subparaneural injections, regardless of nerve expansion. Overall, five studies reported intrafascicular deposits, two of which frequently, following intraneural and subparaneural injections. None of the currently used ultrasound findings was predictive of intrafascicular deposits. CONCLUSIONS: Our results suggest that sonographic parameters of intraneural and subparaneural injections are reliable in terms of detecting spread location. Intrafascicular injectate deposition may occur, albeit infrequently, particularly in the proximal brachial plexus. Our findings support the judicious interrogation of sonographic parameters suggestive of incipient intraneural injection.

Sciatic nerve movement in the deep gluteal space during hip rotations maneuvers.

We hypothesize that the sciatic nerve in the subgluteal space has a specific behavior during internal and external coxofemoral rotation and during isometric contraction of the internal and external rotator muscles of the hip. In 58 healthy volunteers, sciatic nerve behavior was studied by ultrasound during passive internal and external hip rotation movements and during isometric contraction of internal and external rotators. Using MATLAB software, changes in nerve curvature at the beginning and end of each exercise were evaluated for longitudinal catches and axial movement for transverse catches. In the long axis, it was observed that during the passive internal rotation and during the isometric contraction of external rotators, the shape of the curve increased significantly while during the passive external rotation and the isometric contraction of the internal rotators the curvature flattened out. During passive movements in internal rotation, on the short axis, the nerve tended to move laterally and forward, while during external rotation the tendency of the nerve was to move toward a medial and backward position. During the isometric exercises, this displacement was less in the passive movements. Passive movements of hip rotation and isometric contraction of the muscles affect the sciatic nerve in the subgluteal space. Retrotrochanteric pain may be related to both the shear effect of the subgluteus muscles and the endoneural and mechanosensitive aggression to which the sciatic nerve is subjected.

The EFSUMB Guidelines and Recommendations for Musculoskeletal Ultrasound - Part II: Joint Pathologies, Pediatric Applications, and Guided Procedures.

The second part of the Guidelines and Recommendations for Musculoskeletal Ultrasound (MSUS), produced under the auspices of EFSUMB, following the same methodology as for Part 1, provides information and recommendations on the use of this imaging modality for joint pathology, pediatric applications, and musculoskeletal ultrasound-guided procedures. Clinical application, practical points, limitations, and artifacts are described and discussed for every joint or procedure. The document is intended to guide clinical users in their daily practice.

The EFSUMB Guidelines and Recommendations for Musculoskeletal Ultrasound - Part I: Extraarticular Pathologies.

The first part of the guidelines and recommendations for musculoskeletal ultrasound, produced under the auspices of the European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB), provides information about the use of musculoskeletal ultrasound for assessing extraarticular structures (muscles, tendons, entheses, ligaments, bones, bursae, fasciae, nerves, skin, subcutaneous tissues, and nails) and their pathologies. Clinical applications, practical points, limitations, and artifacts are described and discussed for every structure. After an extensive literature review, the recommendations have been developed according to the Oxford Centre for Evidence-based Medicine and GRADE criteria and the consensus level was established through a Delphi process. The document is intended to guide clinical users in their daily practice.

Opening injection pressure monitoring using an in-line device does not prevent intraneural injection in an isolated nerve model.

BACKGROUND: Injection pressure monitoring using in-line devices is affordable and easy to implement into a regional anesthesia practice. However, solid evidence regarding their performance is lacking. We aimed to evaluate if opening injection pressure (OIP), measured with a disposable in-line pressure monitor, can prevent intraneural (subepineural) injection using 15 pound per square inch (PSI) as the reference safety threshold. METHODS: An isolated nerve model with six tibial and six common peroneal nerves from three unembalmed fresh cadavers was used for this observational study. A mixture of 0.5% ropivacaine with methylene blue was injected intraneurally at a rate of 10 mL/min, to a maximum of 3 mL. OIP was recorded for each injection as well as evidence of intraneural contrast. Injected volume at 15 and 20 PSI was recorded, and when it leaked out the epineurium, if it occurred. RESULTS: In all cases, OIP was<15 PSI and intraneural contrast was evident before the safety threshold. The 15-20 PSI mark was attained in 5 of 12 injections (41%), with a median injected volume of 0.9 mL (range 0.4-2.3 mL). Peak pressure of >20 PSI was reached in two injections (at 0.6 mL and 2.7 mL). Contrast leaked out the epineurium in 11 of 12 injections (91%) with a median injected volume of 0.6 mL (range 0.1-1.3 mL). CONCLUSIONS: Our results suggest that in-line pressure monitoring may not prevent intraneural injection using an injection pressure of 15 PSI as reference threshold. Due to the preliminary nature of our study, further evidence is needed to demonstrate clinical relevance.

Anatomical basis of fascial plane blocks.

Fascial plane blocks (FPBs) are regional anesthesia techniques in which the space ("plane") between two discrete fascial layers is the target of needle insertion and injection. Analgesia is primarily achieved by local anesthetic spread to nerves traveling within this plane and adjacent tissues. This narrative review discusses key fundamental anatomical concepts relevant to FPBs, with a focus on blocks of the torso. Fascia, in this context, refers to any sheet of connective tissue that encloses or separates muscles and internal organs. The basic composition of fascia is a latticework of collagen fibers filled with a hydrated glycosaminoglycan matrix and infiltrated by adipocytes and fibroblasts; fluid can cross this by diffusion but not bulk flow. The plane between fascial layers is filled with a similar fat-glycosaminoglycan matric and provides gliding and cushioning between structures, as well as a pathway for nerves and vessels. The planes between the various muscle layers of the thorax, abdomen, and paraspinal area close to the thoracic paravertebral space and vertebral canal, are popular targets for ultrasound-guided local anesthetic injection. The pertinent musculofascial anatomy of these regions, together with the nerves involved in somatic and visceral innervation, are summarized. This knowledge will aid not only sonographic identification of landmarks and block performance, but also understanding of the potential pathways and barriers for spread of local anesthetic. It is also critical as the basis for further exploration and refinement of FPBs, with an emphasis on improving their clinical utility, efficacy, and safety.